Synthetic erythrocytes (hemosomes) are stroma-free hemoglobin solution encapsulated inside artificial phospholipid membrane. Made entirely of materials naturally occurring in blood, they are non-toxic, do not cause allergic or immune reactions, and are normally metabolized. O2-dissociation curve is almost identical to that of erythrocytes. O2 and CO2 carrying capacity appears sufficient to provide adequate transport in circulation. Rats survive more than 24 hours after virtually complete exchange of blood. The absence of proteins in the membrane makes hemosomes a "universal donor," and contributes to improved chemical and mechanical stability, and storage properties, as compared to erythrocytes. The rate of removal from circulation is slow. The tests made so far indicate that hemosommes are a successful oxygen-carrying blood substitute. We propose to produce sterile hemosomes, to prove their ability to sustain life by achieving the long-term survival of animals after washout transfusions, to study whether hemosomes cause any chronic changes in vital organs, to determine effects of hemosomes on hemodynamics, respiration, blood gases, to determine their half-life in-vivo in circulation, to study the change of O2-carrying capacity of hemosomes in circulation as a function of time, and to determine whether they are mechanically destroyed in circulation.